The present invention relates to a method for stiffening and straightening starting sheets by embossing upon the sheet patterns projecting from its plane, and to an apparatus for carrying out the method according to the invention.
For example, the electrolytic refining of copper is carried out by casting impure raw copper into about 40-mm-thick anodes, which dissolve in the electrolyte in the electrolytic cell, and the pure copper is deposited on starting sheets situated between the raw-copper anodes. These starting sheets are thin sheets, in this case copper sheets, having a thickness of approximately 0.4-1.2 mm and a relatively large surface area. For this reason, the starting sheets are very brittle and have to be handled with care so that they will not buckle or bend. The straighter the starting sheets are when they are fitted in the electrolytic cell and the closer the electrodes can be fitted in relation to each other, the higher the capacity of the electrolytic cell. For this reason, it is very important that the thin and brittle starting sheets can be straightened and kept straight during their handling, which includes the attaching of the lugs to the starting sheets and the transfer of the starting sheets into the electrolytic tank.
It is previously known to emboss upon the starting sheet stiffening patterns projecting from its plane, either by pressing or rolling the starting sheet by means of a roller or a press, the opposite surfaces of which have the said patterns for stiffening and straightening the sheet, whereafter the stiffened starting sheets are provided with lugs and are lifted up into a verticle position.
Furthermore, it is known from U.S. Pat. No. 3,544,431 to remove the starting sheets during the process from the electrolytic tank after a suitably thick layer has been deposited on them and to cold work the starting sheets in a press, whereafter the thus straightened sheets are returned to the electrolytic tank for depositing until the final thickness is obtained.
All the methods and apparatus mentioned above have the disadvantage that the sheets cannot be aligned in relation to the lugs. Consequently, when the sheets are lifted up into the vertical position to hang by their lugs, the plane of the sheet can deviate more or less from the vertical direction. In addition, the sheet may be bent and distorted when it is lifted up to hang by its lugs.
The method disclosed in U.S. Pat. No. 3,544,431 has the further disadvantage that the removal of the starting sheet from the electrolytic tank for intermediate straightening is a complicated and expensive step, which can be eliminated in accordance with the present invention.
The object of the present invention is thus to provide a method and apparatus for the stiffening and straightening of starting sheets, wherein the above-mentioned disadvantages have been eliminated and stiffening patterns projecting from the plane of the sheet are embossed upon the starting sheet in such a manner that the starting sheet can at the same time be aligned in relation to the lugs, and wherein the attaching of the lugs and the transfer of the starting sheet into the electrolytic tank do not produce any additional strains or distortion or unevenness in the starting sheet. By means of the present invention it is thus possible to fit the electrodes closer to each other than previously, and thereby to increase the capacity of the electrolytic tank.
A further object of the present invention is to provide a stiffer starting sheet than previously by embossing upon it improved stiffening patterns, the height of which from the plane of the starting sheet is, however, so small that no risk of a short circuit is produced.